This work is a characterization of permeability of Xenopus laevis developing embryos as well as a chromatographic characterization of the tRNA isoacceptors during early development of Xenopus laevis. We have defined conditions for the heretofore unknown permeability of Xenopus embryos to organic metabolites and are continuing to define the system. Specificity exists in the transport of amino acids with a number of transport systems operating. These are being defined by using competitive inhibitors and antibiotics. tRNAAsp isoacceptors are chromatographically altered during development of Xenopus. This is indicitive of a Q base modifying enzyme varying during development. This study is continuing to characterize at 20 amino acid specific tRNA chromotographic profiles on RPC-5 as a function of development to elucidate these alterations in tRNA patterns. BIBLIOGRAPHIC REFERENCE: Hampel, A., Prahlad, K.V., Brei, S.T,, Ruefer, B., and Mlot, C. "Permeability of Xenopus laevis Embryos: Specific Incorporation of Precursors into Eukaryotic Proteins and Nucleic Acids." Developmental Biology 44, 169-177 (1975).